Go script to get the distance between two airports. I may someday make this an App Engine app w/ API, or accumulate multiple trips together. Sometimes I get curious how far I've flown so far this year.

airports.go

package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"log"
	"math"
	"net/http"
)

const (
	r        = 3958.75587 // miles
	degToRad = math.Pi / 180

	clientId     = "TODO"
	clientSecret = "TODO"
	version      = "20130515"
)

var (
	src = flag.String("src", "", "Airport code for source")
	dst = flag.String("dst", "", "Airport code for destination")
)

type latLng struct {
	Lat, Lng float64
}

func main() {
	flag.Parse()

	fmt.Printf("%g miles", distance(*getLatLng(*src), *getLatLng(*dst)))
}

// http://en.wikipedia.org/wiki/Haversine_formula
func distance(src, dst latLng) float64 {
	dLat := (src.Lat - dst.Lat) * degToRad
	dLng := (src.Lng - dst.Lng) * degToRad
	srcLat := src.Lat * degToRad
	dstLat := dst.Lat * degToRad

	a := math.Pow(math.Sin(dLat/2), 2) + math.Pow(math.Sin(dLng/2), 2)*math.Cos(srcLat)*math.Cos(dstLat)
	c := 2 * math.Atan2(math.Sqrt(a), math.Sqrt(1-a))
	return r * c
}

// Foursquare API response
type response struct {
	Response struct {
		Venues []struct {
			Location latLng
		}
	}
}

func getLatLng(airportCode string) *latLng {
	url := fmt.Sprintf(
		"https://api.foursquare.com/v2/venues/search?intent=global&query=%s+airport&limit=1&client_id=%s&client_secret=%s&v=%s",
		airportCode, clientId, clientSecret, version)

	resp, err := http.Get(url)
	if err != nil {
		log.Fatal(err)
	}
	defer resp.Body.Close()

	var r response
	err = json.NewDecoder(resp.Body).Decode(&r)
	if err != nil {
		log.Fatal(err)
	}

	if len(r.Response.Venues) == 0 {
		log.Fatal("Error getting airport location")
	}

	return &r.Response.Venues[0].Location
}